THE NATURE OF BLOOD LIPIDS 357 



cloud point studies, also, he excludes serum 7-globulin, insulin, diphtheria 

 toxin, diphtheria antitoxin, and papain from the group of proteins which 

 manifest the property of combination with fatty acids. 



The best basis for the specificity of serum albumin in binding anions 

 would seem to be that it contains a number of positively charged groups. 

 That this is the case is indicated by the more recent results of Teresi, 45 

 in which it was demonstrated that, when the free e-amino groups of lysine 

 are eliminated, the number of ions of m-nitrophenolate or p-nitrophenolate 

 bound by the modified protein is markedly reduced. In the case of the 

 o-nitrophenolates (mono-, di-, or trinitro-), no reduction in binding power 

 followed the treatment of the protein with formaldehyde, or its acetylation. 

 This is interpreted as evidence that the guanidine residues may likewise 

 be concerned in the combinations. 



In addition to the electrostatic forces, Luck s believes that the experi- 

 ments of Boyer et a 7 . 32 prove the importance of the van der Waals' forces as 

 explaining the binding effects. On the other hand, Klotz and Urquhart 44 

 proposed the theory that the binding capacity of a protein is a direct func- 

 tion of the number of positively charged groups and an inverse function of 

 the number of carboxyl and hydroxyl groups. As a result of his experi- 

 ments on methyl orange, Klotz and Urquhart 46 feel that the van der Waals' 

 forces play only a minor role. Luck 8 does not accept the latter deduction, 

 since the dye is believed to be atypical, and conclusions obtained from it are 

 not applicable to the binding of fatty acids by proteins. 



{2) Neutral Fats 



Despite extensive knowledge of the fatty acid makeup of the blood, little 

 is known of the nature of the neutral fat component or of the nature of the 

 fatty acid moiety which is normal^ combined with glycerol. Since the 

 neutral fats are much less soluble than the other lipid components of plasma, 

 they exist as finely emulsified droplets called chylomicrons, 3 which are gen- 

 erally not more than 1.0 m in diameter. 47 According to Frazer, 48 blood 

 collected after a twelve-hour starvation period contains only a trace of fatty 

 acids and triglycerides. In hyperlipemic blood, the glyceryl esters are 

 considerably increased, without any appreciable alteration in the free 

 fatty acids. The neutral fat consists chiefly of glycerol esters of C12 to Ci 8 



45 J. D. Teresi, J. Am. Chem. Soc, 72, 3972-3978 (1950). 



46 1. M. Klotz and J. M. Urquhart, /. Am. Chem. Soc, 71, 847-851 (1949). 



47 E. S. West and W. R. Todd, Textbook of Biochemistry, Macmillan, New York, 1951. 



48 A. C. Frazer, in Lipoproteins, General discussion Faraday Soc, No. 6, 81-97, 

 Aberdeen Univ. Press, Aberdeen, 1949. 



